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Transcript
Digestive System
Obtaining nutrients
Energy
• Body cells need energy to run cell
processes.
• Animals obtain chemical energy from
food. Energy is derived from breaking
chemical bonds.
• Food energy is measured in units called
calories.
Lipids
• Lipids are fats, oils, and
waxes.
• Lipids are energy
dense, containing 9
calories per gram.
• Lipids are used for
storing energy, making
cell membranes, and
synthesizing steroid
hormones.
Many lipids are made up of
fatty acids and glycerine.
Carbohydrates
• Sugars and starch are
the carbohydrates that
humans can digest.
“Fiber” is indigestible
carbohydrates, such as
cellulose and inulin.
• Glucose is needed by
all body cells as energy.
Nerve cells must have
glucose to operate.
Starch is made up of glucose.
Proteins
• Amino acids from
digested proteins are
used by cells to build all
the proteins that our
body needs.
• Humans need a balance
of the 20 amino acids,
which can be obtained
from animal proteins, or
by blending plant
protein sources.
Proteins are made up of
amino acids.
Macromolecule summary
Polymers
Complex
Carbohydrates
(i.e. starch)
Monomers
Roles
Glucose and other Broken apart to get energy to
simple sugars
make ATP.
Proteins
Amino acids
Used to make our own
enzymes and other body
proteins.
Lipids (Fats,
waxes, oils, and
steroids)
Fatty acid chains,
glycerine (except
steroids)
Used for cellular energy and
energy storage; used to make
cell membranes, steroid
hormones.
Minerals
• Sodium, potassium,
zinc, iron, calcium,
copper, and selenium
are among the
minerals that humans
need.
• Most minerals can be
found in whole grains,
fruits, vegetables, nuts,
and meats. Highly
processed foods may
be deficient.
Major Minerals
Mineral
Major roles
Natural sources
Calcium
Bone and tooth formation; muscle
and nerve function.
Dairy products, leafy greens, dry
beans.
Iron
Used to make hemoglobin and
myoglobin.
Red meats, eggs, nuts, whole
grains, leafy greens.
Zinc
Component of certain enzymes,
required for growth.
Meats, whole grains, nuts, legumes.
Phosphorous
Bone and tooth formation; pH of body Dairy products, grains.
fluids, phospholipids.
Potassium
Maintains pH of body fluids; used in
action potentials.
Many fruits and vegetables, meats,
milk.
Sodium
Maintains pH of body fluids; used in
action potentials.
Table salt, meats.
Selenium
Used by the immune system.
Nuts, esp. Brazil nuts; many fruits
and vegetables.
Vitamins
• Vitamins play many
different roles in
metabolism.
• We do not obtain
energy from vitamins;
however, some
vitamins are necessary
to run energy-related
processes in cells.
Major Vitamins
Vitamins
Major roles
Natural sources
Vitamin A (fat
soluble
Used to make visual pigments;
maintains epithelial tissues; needed
for normal growth.
Orange and yellow fruits and
vegetables, egg yolk, dairy
products.
B complex vitamins
(water soluble)
Used in cellular respiration to
metabolize sugars and other carbon
compounds.
Whole grains, legumes, many
fruits and vegetables. B12 comes
from animal sources.
Vitamin C (water
soluble)
Used in collagen synthesis, possible
role in immune function.
Fresh fruits and vegetables.
Vitamin D (fat
soluble)
Bone growth, calcium absorption,
possible role in immune function.
Eggs, dairy products. Sunlight on
skin oils creates Vitamin D.
Vitamin E (fat
soluble)
Antioxidant, reduces cellular
damage.
Nuts, whole grains, leafy
vegetables.
Vitamin K
Plays a role in blood clotting.
Produced by intestinal bacteria.
Digestion
Two-way digestion
• Simple animals have a
single digestive pouch
with a single opening.
• Food enters through
the opening, waste
leaves through the
same opening.
• These organisms must
finish digesting before
eating again.
One-way digestion
• More complex animals
have one-way
digestion.
• Food enters one
opening and waste
leaves from another.
• Animals with one-way
systems can eat any
time, which is an
advantage.
Mechanical digestion
• In humans, mechanical
digestion takes place in the
mouth.
• Human incisors and
canines are adapted for
tearing food, while molars
are adapted for grinding
food.
• Saliva, which contains
enzymes, mixes with food.
Esophagus
• After food is
proccessed by the
mouth it is passed
to the pharynx.
• The pharynx is an
open area at the
back of the mouth.
Esophagus
• From the pharynx a
flap of tissue called
the epiglottis
prevents food from
going down the
trachea (wind pipe).
• Food is forced into
the Esophagus by
swalling
Esophagus
• The Esophagus has
an inner muscle
layer and an outer
muscle layer. The
two layers alternate
contractions
causing the
swallowing action or
peristalsis.
Stomach
• The stomach
digests food by
mechanical and
chemical processes.
• First the many
muscles making up
the stomach
continually churn of
food.
Stomach
• Gastric Pits (the
openings of glands)
Secrete acids, enzymes
and mucus.
• Pepsin, an enzyme that
breaks up proteins,
requires an acidic
environment to become
active.
• Hydrochloric Acid is
produced in the pits.
Stomach
• At the top of the
stomach the
Cardiac Sphincter
keeps food from
coming back up.
• At the bottom of the
stomach the Pyloric
Sphincter keeps
food in until it’s fully
turned into Chyme.
Duodenum
•
digestion continues in
the upper small intestine,
the duodenum.
• Enzymes that will
continue the digestion
need a basic (non
Acidic) environment.
• The pancreas and liver
secrete chemicals that
turn the acid into a bas.
Pancreas and Liver
• Pancreas releases
pancreatic juice,
containing bicarbonate,
lipases, proteases, and
amylase.
• The liver makes bile,
which emulsifies fats.
Bile is made from
cholesterol, which is
made in the liver.
Small intestine
• The walls of the small
intestine are lined with
millions of microvilli.
This is the site of
nutrient absorption.
• Small intestines also
produce many digestive
enzymes to break large
polymers completely
down into monomers.
Villi and microvilli
Digestion and pH
Location
pH
Enzymes
Molecules digested
Mouth
neutral
Amylase
Starch
Stomach
acidic
Pepsin (a peptidase)
Initial protein
digestion
Small intestine
Basic to neutral
Mixture of amylase,
peptidases, lipases
Digestion of
starches, final
breakdown of
proteins, digestion of
lipids.
Large intestine
• Water from digested food
is absorbed in the large
intestine.
• Bacteria present in the
large intestine feed on
unabsorbed nutrients, and
produce several vitamins.
• Fecal material is formed
from fiber and other
undigested material.
Hormones and digestion
• Many hormones produced by the digestive system
itself are responsible for appetite and digestion.
• Gastrin in the stomach, produced when food is present,
signals release of acid.
• Secretin signals the release of sodium bicarbonate by
the pancreas.
• Ghrelin and Leptin, recently discovered, control
appetite. Changes in these hormones cause
overeating, because people with too little of these
hormones don’t realize they’re full.